It is hard to understand why a man as accomplished as the octogenarian Lester Wunderman - the so-called "inventor of direct marketing" - still pounds the boards of agencies, extolling the virtues of an industry he helped to found.
You'd think by now, with DM growing at such a pace, that he would want to relax and enjoy the fruits of his 50-year-long career.
But, at 85, Wunderman is still on the payroll of the WPP-owned agency he founded as its chairman emeritus. He describes his role as strategist and missionary for the discipline but without the stress of worrying about profit and losses. Retirement seems a long way off.
His critics, while acknowledging his role in establishing the term "direct marketing", think his relevance to the market today is limited.
Despite his years, though, he hasn't taken his eye off the ball. The new version of his book, Being Direct: Making Advertising Pay, first published in 1996, now includes a 19-point "Consumers' Bill of Rights". This acknowledges that, because the internet and associated technology have given advertisers greater access to consumers' lives, they need to respect some boundaries.
"Advertisers get more information from consumers. If they're skilful, they use the information in a relevant way. If they're not, they'll use it in an invasive way. So I thought there should be a set of rules for advertisers to follow that would create a pact between us and the consumer," he says.
So the bill includes "rules" such as "don't assume I want to have a relationship with you" and "make my shopping experience easier."
But, despite his concerns, Wunderman has lost none of his passion for DM. His original vision remains unchanged.
Wunderman's view is that branding and positioning are the responsibilities of ad agencies, while direct marketers should concentrate on what they're good at - building relationships with customers and learning about their behaviour.
"Where DM agencies come in is creating a brand experience, and this is much deeper than identity or description. So we become a vital part of the brand experience and I think that's where the action is and will continue to be," he says.
This may be an idea that some below-the-line creatives, who believe they are capable of taking on their above-the-line counterparts, baulk at. But it marks out why DM is growing faster than advertising, and perhaps also explains the growing popularity of greater collaboration between the two disciplines.
"All the divides that have gone up in the industry will eventually come down. Advertising is a very holistic process. And those who don't practice it holistically are going to fail," Wunderman says.
As well as displaying an awareness of the issues facing DM, it is his belief in the power of the medium that provides leadership to an industry that all too often lacks the confidence to bang its own drum.
"The power of DM will prevail; whether or not the constituent parts have the confidence, the truth will out. DM will out-pace general advertising.
Advertising is a product of the industrial revolution; we are a product of the information age. Our dynamic is stronger, more vital, younger and more energetic than the dynamics of general advertising," he concludes.